Polycarboxylic acid copolymers have been used as components of cement additives for cement compositions such as cement paste, mortar, and concrete. They are now essential in constructing civil engineering and building structures and the like from cement compositions. Cement additives comprising such polycarboxylic acid copolymers are used as water reducing agents; they increase the fluidity of cement compositions to thereby reduce the water requirement of the cement compositions and therefore are effective in improving the strength, durability, and the like, of hardening products. Such water reducing agents are superior in water reducing capacity to naphthalene-based and other conventional water reducing agents and thus have already led to good results in many cases as air-entraining and high-range water-reducing admixture.
Meanwhile, foundations and like parts of civil engineering and building structures are required to have high strength or durability and, therefore, the so-called ultrahigh strength concrete compositions having high performance characteristics among concrete species are used in constructing them. As water reducing agents for such ultrahigh strength concrete, use is made of water reducing agents for ultrahigh strength concrete, which are high in water reducing capacity, so that the amount of water in concrete can be reduced to a sufficient extent to attain high performance characteristics. Currently, copolymers of methacrylic acid and polyethylene oxide methacrylate, for instance, are in use as water reducing agents for ultrahigh strength concrete. However, when an ultrahigh strength concrete is produced using such a water reducing agent for ultrahigh strength concrete, the concrete shows a high viscosity. Therefore, water reducing agents for ultrahigh strength concrete which can improve the workability are demanded.
In the specification of Japanese Kokai Publication Hei-07-215746, there is disclosed the use, as water reducing agents, of copolymers of an alkenyl ether, which has oxyalkylene group containing 2 to 40 carbon atoms and its end essentially has an alkenyl group and a specific group containing 1 to 24 carbon atoms, and maleic anhydride. However, for their successful application as water reducing agents for ultrahigh strength concrete, in particular, there is room for contrivance concerning the copolymer structure and characteristics.
Japanese Kokai Publication 2000-191356 discloses that a cement dispersant whose main component is a water-soluble amphoteric copolymer obtained by copolymerization of a specific polyamine-derived monomer as compound A, a specific unsaturated carboxylic acid monomer as compound B and a specific polyalkylene glycol-derived monomer as compound C in the proportion compound A:compound B:compound C=10 to 40% by weight:10 to 40% by weight:50 to 80% by weight can be used as a dispersant for ultrahigh strength concrete and that it is excellent in field workability.
However, water-soluble amphoteric copolymers prepared in all Examples in this publication by copolymerizing compound A, compound B and compound C, when used in preparing high strength concrete, provide them with high viscosity, making the shovel work difficult; thus, they have a workability problem.